Signal conversion

ABSTRACT

A circuit may include an input terminal configured to receive an input signal with a first voltage swing and an output terminal. The circuit may also include a first transistor, a second transistor, a third transistor, and a control circuit. The control circuit may be coupled to the input terminal, a gate terminal of the first transistor, and a gate terminal of the second transistor. The control circuit may be configured to adjust voltages provided to the gate terminals based on the input signal such that the first transistor conducts in response to the input signal being at a first logical level and the second transistor conducts in response to the input signal being at a second logical level to generate an output signal output on the output terminal. The second voltage swing of the output signal may be different from the first voltage swing of the input signal.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 62/018,792, filed Jun. 30, 2014, which isincorporated herein by reference.

FIELD

The embodiments discussed herein are related to signal conversion.

BACKGROUND

Different signaling standards may be used in circuits to transmit data.The different signaling standards may include current-mode-logic (CML),complementary metal-oxide-semiconductor (CMOS), transistor-transistorlogic (TTL), low voltage TTL (LVTTL), emitter-coupled logic (ECL), amongothers types of signaling standards. A signaling standard may beselected for a design based on circuitry, logic, and/or signaling speedsfor the design. In some circumstances, a design may use two or moresignaling standards. For example, the CML standard may be used totransmit data signals between modules in a design and the CMOS standardmay be used when processing the data signals within the modules. Inthese circumstances, the data signals may be converted from the CMLstandard to the CMOS standard.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one exemplary technology area where some embodimentsdescribed herein may be practiced.

SUMMARY

Some example embodiments generally relate to signal conversion.

In an example embodiment, a circuit may include an input terminalconfigured to receive an input signal with a first voltage swing and anoutput terminal configured to output an output signal with a secondvoltage swing that is different than the first voltage swing. Thecircuit may also include first, second, and third transistors, anamplifier, a first resistance, and a second resistance. The firsttransistor may include a first gate terminal and a first drain terminal.The first gate terminal may be coupled to the input terminal. The secondtransistor may include a second gate terminal, a second source terminal,and a second drain terminal. The second source terminal may be coupledto the first drain terminal. The amplifier may include first and secondamplifier input terminals and an amplifier output terminal. Theamplifier output terminal may be coupled to the second gate terminal.The second amplifier input terminal may be configured to receive acontrol voltage. The first resistance may be coupled between the secondsource terminal and the second amplifier input terminal. The thirdtransistor may include a third gate terminal, a third source terminal,and a third drain terminal. The third source terminal may be coupled toa first voltage and the third drain terminal may be coupled to theoutput terminal. The second resistance may be coupled between the thirdgate terminal and the amplifier output terminal. The fourth transistormay include a fourth gate terminal, a fourth source terminal, and afourth drain terminal. The fourth source terminal may be coupled to asecond voltage, the fourth drain terminal may be coupled to the outputterminal, and the fourth gate terminal may be coupled to the seconddrain terminal.

In yet another example embodiment, a circuit may include an inputterminal configured to receive an input signal with a first voltageswing and an output terminal. The circuit may also include a firsttransistor, a second transistor, a third transistor, and a controlcircuit. The first transistor may include a first gate terminal, a firstsource terminal, and a first drain terminal. The second transistor mayinclude a second gate terminal, a second source terminal, and a seconddrain terminal. The second drain terminal may be coupled to the outputterminal and the second source terminal may be coupled to a firstvoltage. The third transistor may include a third gate terminal, a thirdsource terminal, and a third drain terminal. The third drain terminalmay be coupled to the output terminal, the third source terminal may becoupled to a second voltage, and the third gate terminal may be coupledto the first drain terminal. The control circuit may be coupled to theinput terminal, the first gate terminal, and the second gate terminal.The control circuit may be configured to adjust voltages provided to thefirst gate terminal and the second gate terminal based on the inputsignal such that the second transistor conducts in response to the inputsignal being at a first logical level and the third transistor conductsin response to the input signal being at a second logical level togenerate an output signal output on the output terminal. As a result,the second voltage swing of the output signal may be different from thefirst voltage swing of the input signal.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential characteristics of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

Additional features and advantages of the invention will be set forth inthe description that follows or may be learned by the practice of theinvention. The features and advantages of the invention may be realizedand obtained by means of the instruments and combinations particularlypointed out in the appended claims. These and other features of thepresent invention will become more fully apparent from the followingdescription and appended claims, or may be learned by the practice ofthe invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the invention will be rendered byreference to embodiments thereof, which are illustrated in the appendeddrawings. It is appreciated that these drawings depict only someembodiments of the invention and are therefore not to be consideredlimiting of its scope. The invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1A illustrates an example signal conversion circuit;

FIG. 1B illustrates a graph with two differential signals;

FIG. 2A illustrates another example signal conversion circuit;

FIG. 2B illustrates an example implementation of a control circuit inthe signal conversion circuit of FIG. 2A;

FIG. 3A illustrates another example signal conversion circuit;

FIG. 3B illustrates an example implementation of a control circuit inthe signal conversion circuit of FIG. 3A; and

FIG. 4 is a perspective view of an example optoelectronic module where asignal may be converted.

DETAILED DESCRIPTION

FIG. 1A illustrates an example signal conversion circuit 100 (“thecircuit 100”), arranged in accordance with at least some embodimentsdescribed herein. In general, the circuit 100 may be configured toreceive a first differential signal and convert the first differentialsignal to a second differential signal. The second differential signalmay include a voltage swing that is different from a voltage swing ofthe first differential signal. In particular, the voltage swing of thesecond differential signal may be greater than the voltage swing of thefirst differential signal. In these and other embodiments, a voltageswing of the differential signal may refer to a difference between avoltage that represents a logical low value of data carried by thedifferential signal and a voltage that presents a logical high value ofdata carried by the differential signal.

FIG. 1B illustrates a graph 150 with a first differential signal 160 anda second differential signal 170 and their respective voltage swings,arranged in accordance with at least some embodiments described herein.The first differential signal 160 may include a first signal 160 a and asecond signal 160 b. The second differential signal 170 may include afirst signal 170 a and a second signal 170 b. The graph 150 may furtherillustrate a first voltage swing 166 of the first differential signal160 and a second voltage swing 176 of the second differential signal170. As illustrated, the first voltage swing 166 may be larger than thesecond voltage swing 176.

Referring again to FIG. 1A, the circuit 100 may include first and secondinput terminals 102 and 103, first and second output terminals 104 and105, a control circuit 110, and first, second, third, and fourthtransistors 112-115. Each of the transistors may include a gateterminal, a source terminal, and a drain terminal. As illustrated inFIG. 1, the source terminal may be the terminal with the arrow, the gateterminal may be the terminal with the parallel horizontal lines, and thedrain terminal may be the other terminal.

The first and second input terminals 102 and 103 may be coupled to thecontrol circuit 110. The control circuit 110 may be coupled to the gateterminals of each of the first, second, third, and fourth transistors112-115. Source terminals of each of the first and second transistors112 and 113 may be coupled to a first voltage V1. Source terminals ofeach of the third and fourth transistors 114 and 115 may be coupled to asecond voltage V2. Drain terminals of the first transistor 112 and thethird transistor 114 may be coupled to the first output terminal 104.Drain terminals of the second transistor 113 and the fourth transistor115 may be coupled to the second output terminal 105.

The first and second input terminals 102 and 103 may be configured toprovide an input differential signal to the control circuit 110. Thecontrol circuit 110 may be configured to adjust the voltages on the gateterminals of each of the first, second, third, and fourth transistors112-115 based on the received input differential signal to generate anoutput differential signal on the first and second output terminals 104and 105. The voltage swing of the output differential signal may bebetween the first voltage V1 and the second voltage V2. In these andother embodiments, the voltage swing of the output differential signalmay be larger than a voltage signal of the input differential signal. Insome embodiments, the voltage swing of the output differential signalmay include a middle value that is equal or approximately equal to amiddle value of the voltage swing of the input differential signal.Alternately or additionally, the middle value of the voltage swing ofthe output differential signal may be offset from the middle value ofthe voltage swing of the input differential signal. In these and otherembodiments, the voltage swing of the output differential signal may bebetween the first voltage and the second voltage. In some embodiments,the second voltage may be at ground potential, e.g., approximately zerovolts or zero volts. When discussing voltage swings of the outputdifferential signal, a value that is approximately zero, in someembodiments, may be a value that is within a range between −0.4 and 0.4.

An example of the circuit 100 generating the output differential signalfollows. A first input signal of the input differential signal may be alogical high and a second input signal of the input differential signalmay be a logical low. The circuit 100 may generate a first output signalof the output differential signal on the first output terminal 104 thatis a logical high and may generate a second output signal of the outputdifferential signal on the second output terminal 105 that is a logicallow.

To generate the first output signal, the control circuit 110 may set agate voltage at the gate terminal of the third transistor 114 such thatthe third transistor 114 does not conduct and may set a gate voltage atthe gate terminal of the first transistor 112 such that the firsttransistor 112 conducts. As a result, the first output terminal 104 maybe pulled to the first voltage V1, which may represent a logical highfor the first output signal.

As used herein, the phrase “gate voltage” may refer to a voltage at agate of a transistor. The phrase “source voltage” may refer to a voltageat a source of a transistor and the phrase “drain voltage” may refer toa voltage at a drain of a transistor.

Furthermore, as used herein, the term “conduct” with respect to atransistor indicates that the transistor is in a non-cut-off region ofoperation, such as the linear or saturation region of operation, suchthat current flows between a source and a drain of the transistor. Thus,when a transistor is described as conducting or that it conducts, thetransistor is in a non-cut-off region of operation. In contrast, when atransistor is described as not conducting or that it does not conduct,the transistor is in a cut-off region of operation such that highimpedance is presented at a drain and a source of the transistor.

To generate the second output signal, the control circuit 110 may set agate voltage of the second transistor 113 such that the secondtransistor 113 does not conduct and may set a gate voltage of the fourthtransistor 115 such that the fourth transistor 115 conducts. As aresult, the second output terminal 105 may be pulled to the secondvoltage V2, which may represent a logical low for the first outputsignal. In this manner, the circuit 100 may generate the outputdifferential signal that includes a voltage swing between the first andsecond voltages V1 and V2 that is larger than a voltage swing of theinput differential signal. As an example, the input differential signalmay be a current-mode-logic (CML) signal and the output differentialsignal may be a complementary metal-oxide-semiconductor (CMOS) signal.

Modifications, additions, or omissions may be made to the circuit 100without departing from the scope of the present disclosure. For example,additional active or passive circuit elements may be included in thecircuit 100.

FIG. 2A illustrates another example signal conversion circuit 200 (“thecircuit 200”), arranged in accordance with at least some embodimentsdescribed herein. In general, the circuit 200 may be configured toreceive an input differential signal and convert the input differentialsignal to an output differential signal. The output differential signalmay include a voltage swing that is different from a voltage swing ofthe input differential signal. In particular, the voltage swing of theoutput differential signal may be between a first voltage V1 and asecond voltage V2 and may be greater than the voltage swing of the inputdifferential signal. In these and other embodiments, both the firstvoltage and the second voltage may be non-ground potential voltages. Insome embodiments, both the first and second voltages may be lower thanthe lowest voltage of the input differential signal or may be higherthan the highest voltage of the input differential signal. Alternatelyor additionally, one of the first and second voltages may be within thevoltage swing of the input differential signal.

The circuit 200 may include first and second input terminals 202 and203, first and second output terminals 204 and 205, a control voltageterminal 206, a control circuit 210, first, second, third, fourth,fifth, sixth, seventh, eighth, ninth, and tenth transistors 220-229,referred to herein collectively as the transistors 220-229, a duty cyclesense circuit 230, and a first current source 240.

Each of the transistors 220-229 may include a gate terminal, a sourceterminal, and a drain terminal. As illustrated in FIG. 2A, the sourceterminal may be the terminal with the arrow, the gate terminal may bethe terminal with the parallel horizontal lines, and the drain terminalmay be the other terminal. As illustrated in FIG. 2A, the first, second,third, sixth, seventh, and eighth transistors 220, 221, 222, 225, 226,and 227 may include n-type transistors. The fourth, fifth, ninth, andtenth transistors 223, 224, 228, and 229 may include p-type transistors.

A gate terminal of the first transistor 220 may be coupled to the firstinput terminal 202. A source terminal of the first transistor 220 may becoupled to the first current source 240. A drain terminal of the firsttransistor 220 may be coupled to a source terminal of the secondtransistor 221.

A gate terminal of the second transistor 221 may be coupled to thecontrol circuit 210. A drain terminal of the second transistor 221 maybe coupled to a drain terminal of the fifth transistor 224, a gate ofthe fifth transistor 224, and to a gate of the fourth transistor 223.Source terminals of the fourth and fifth transistors 223 and 224 may becoupled to the second voltage V2. A drain terminal of the fourthtransistor 223 may be coupled to the first output terminal 204 and to adrain terminal of the third transistor 222. A gate terminal of the thirdtransistor 222 may be coupled to the control circuit 210. A sourceterminal of the third transistor 222 may be coupled to the first voltageV1. The first voltage V1 may be lower than the second voltage V2.

A gate terminal of the sixth transistor 225 may be coupled to the secondinput terminal 203. A source terminal of the sixth transistor 225 may becoupled to the first current source 240. A drain terminal of the sixthtransistor 225 may be coupled to a source terminal of the seventhtransistor 226.

A gate terminal of the seventh transistor 226 may be coupled to thecontrol circuit 210. A drain terminal of the seventh transistor 226 maybe coupled to a drain terminal of the ninth transistor 228, a gate ofthe ninth transistor 228, and to a gate of the tenth transistor 229.Source terminals of the ninth and tenth transistors 228 and 229 may becoupled to the second voltage V2. A drain terminal of the tenthtransistor 229 may be coupled to the second output terminal 205 and to adrain terminal of the eighth transistor 227. A gate terminal of theeighth transistor 227 may be coupled to the control circuit 210. Asource terminal of the eighth transistor 227 may be coupled to the firstvoltage V1.

The control circuit 210 may be coupled to the first and second inputterminals 202 and 203 and to the control voltage terminal 206. The dutycycle sense circuit 230 may be coupled to the control voltage terminal206 and the first and second output terminals 204 and 205.

The control circuit 210 may be configured to control gate voltages ofthe third and eighth transistors 222 and 227 to control whether thethird and eighth transistors 222 and 227 conduct or do not conduct. Thecontrol circuit 210 may also be configured to control the gate voltagesof the second and seventh transistors 221 and 226 to control whether thesecond and seventh transistors 221 and 226 conduct or do not conduct. Bycontrolling when the second, third, seventh, and eighth transistors 221,222, 226, and 227 conduct, the control circuit 210 may control thegeneration of the output differential signal that is output on the firstand second output terminals 204 and 205.

In particular, the control circuit 210 may be configured to adjust thegate voltages of the second, third, seventh, and eighth transistors 221,222, 226, and 227 based on the input differential signal to control thegeneration of the output differential signal. For example, the inputdifferential signal may include first and second input signals. Thecontrol circuit 210 may adjust the gate voltages of the second and thirdtransistors 221 and 222 based on a logical level of the first inputsignal to generate a first output signal of the output differentialsignal that is output on the first output terminal 204. The controlcircuit 210 may also adjust the gate voltages of the seventh and eighthtransistors 226 and 227 based on a logical level of the second inputsignal to generate a second output signal of the output differentialsignal that is output on the second output terminal 205.

In these and other embodiments, the control circuit 210 may adjust thegate voltages of the second, third, seventh, and eighth transistors 221,222, 226, and 227 based on the input differential signal such that theoutput differential signal includes a signal pattern that corresponds toa signal pattern of the input differential signal. In these and otherembodiments, a corresponding signal pattern may indicate that the outputdifferential signal includes logical highs and logical lows that matchor are an inverse of the logical highs and logical lows of the inputdifferential signal.

An example of the operation of the circuit 200 follows based on thefirst input signal being a logical high and the second input signalbeing a logical low. The first input signal may be received by thecontrol circuit 210. When the first input signal is a logical high, thecontrol circuit 210 may adjust the gate voltage of the third transistor222 such that the third transistor 222 does not conduct and provides ahigh impedance at its drain terminal coupled to the first outputterminal 204. The control circuit 210 may also adjust the gate voltageof the second transistor 221 such that the second transistor 221conducts. The logical high at the gate terminal of the first transistor220 may also cause the first transistor 220 to conduct. The fifthtransistor 224 with its gate terminal coupled to its drain terminal andwith the first and second transistors 220 and 221 conducting may alsoconduct such that current flows from the second voltage V2 through thefirst current source 240 to ground. The fourth transistor 223 may be ina current mirror configuration with the fifth transistor 224. As aresult, when the fifth transistor 224 conducts, the fourth transistor223 may also conduct. As the fourth transistor 223 conducts current fromits source terminal to its drain terminal, the current may build at thefirst output terminal 204, raising the voltage at the first outputterminal 204 to the second voltage V2 such that the first output signalis output as a logical high.

When the second input signal is a logical low, the control circuit 210may adjust the gate voltage of the seventh transistor 226 such that theseventh transistor 226 does not conduct. Furthermore, the logical low atthe gate terminal of the sixth transistor 225 may cause the sixthtransistor 225 to not conduct. As a result, the ninth transistor 228does not conduct. The tenth transistor 229 may be in a current mirrorconfiguration with the ninth transistor 228 and thus does not conduct.As a result, the tenth transistor 229 may provide a high impedance atits drain terminal coupled to the second output terminal 205.

Furthermore, when the second input signal is a logical low, the controlcircuit 210 may adjust the gate voltage of the seventh transistor 226such that the seventh transistor 226 conducts. As the seventh transistor226 conducts current from its source terminal to its drain terminal, thecurrent may build at the second output terminal 205, dropping or raisingthe voltage at the second output terminal 205 to the first voltage V1.Thus, the second output signal may be output as a logical low and thevoltage swing of the output differential signal may be the differencebetween the first and second voltages V1 and V2. In response to thefirst input signal switching to a logical low and the second inputsignal switching to a logical high, the control circuit 210 may beconfigured to adjust the gate voltages such that the first output signalis a logical low and the second output signal is a logical high in asimilar manner as described above.

The duty cycle sense circuit 230 may be coupled to the first and secondoutput terminals 204 and 205 and may be configured to receive the outputdifferential signal. The duty cycle sense circuit 230 may be configuredto detect a duty cycle of the output differential signal. A duty cyclemay relate to an amount of time that the output differential signal isat a logical high level with respect to an amount of time that theoutput differential signal is at a logical low level. The duty cyclesense circuit 230 may compare the detected duty cycle to a particularduty cycle. In response to the detected duty cycle being different fromthe particular duty cycle, the duty cycle sense circuit 230 maydetermine how to correct the duty cycle of the output differentialsignal. The detected duty cycle may be different from the particularduty cycle due to process variations when manufacturing the transistors220-229, circuit variations such as temperature, voltage levels,electromagnetic interface, among others. The duty cycle sense circuit230 may send an indication of the correction to the control circuit 210.

The control circuit 210 may receive the indication of the correction.Based on the indication, the control circuit 210 may adjust when one ormore of the second, third, seventh, and eighth transistors 221, 222,226, and 227 conducts in response to the input differential signal toadjust the duty cycle of the output differential signal. For example,the control circuit 210 may delay adjusting the gate voltages of thesecond, third, seventh, and eighth transistors 221, 222, 226, and 227 inresponse to the input differential signal to adjust the duty cycle ofthe output differential signal with respect to the input differentialsignal.

Modifications, additions, or omissions may be made to the circuit 200without departing from the scope of the present disclosure. For example,additional active or passive circuit elements may be included in thecircuit 200. Alternately or additionally, the circuit 200 may notinclude the duty cycle sense circuit 230. In these and otherembodiments, the circuit 200 may not include the control voltageterminal 206.

FIG. 2B illustrates an example implementation of the control circuit 210of the signal conversion circuit 200 of FIG. 2A, arranged in accordancewith at least some embodiments described herein. The control circuit 210may include a first control transistor 211, a second control transistor212, a first resistance 213, a second resistance 214, a third resistance215, a fourth resistance 216, a differential amplifier 217, and a secondcurrent source 218.

Each of the control transistors 211 and 212 may include a gate terminal,a source terminal, and a drain terminal. As illustrated in FIG. 2B, thesource terminal may be the terminal with the arrow, the gate terminalmay be the terminal with the parallel horizontal lines, and the drainterminal may be the other terminal. As illustrated in FIG. 2B, thecontrol transistors 211 and 212 may be n-type transistors.

A gate terminal of the first control transistor 211 may be coupled tothe first input terminal 202. A source terminal of the first controltransistor 211 may be coupled to the second current source 218. Thedrain terminal of the first control transistor 211 may be coupled to thegate terminal of the third transistor 222 and to a first end of thethird resistance 215. A second end of the third resistance 215 may becoupled to a fourth node N4 to which the gate terminals of the secondand seventh transistors 221 and 226 and an output terminal of thedifferential amplifier 217 are also coupled.

A gate terminal of the second control transistor 212 may be coupled tothe second input terminal 203. A source terminal of the second controltransistor 212 may be coupled to the second current source 218. Thedrain terminal of the second control transistor 212 may be coupled tothe gate terminal of the eighth transistor 227 and to a first end of thefourth resistance 216. The second end of the fourth resistance 216 maybe coupled to the fourth node N4.

A first end of the first resistance 213 may be coupled to the drainterminal of the first transistor 220 and the source terminal of thesecond transistor 221 at a first node N1. The second end of the firstresistance 213 may be coupled to a second end of the second resistance214 and to a first input terminal of the differential amplifier 217 at athird node N3. The first end of the second resistance 214 may be coupledto the drain terminal of the sixth transistor 225 and the sourceterminal of the seventh transistor 226 at a second node N2. A secondinput terminal of the differential amplifier 217 may be coupled to thecontrol voltage terminal 206.

In general, the differential amplifier 217 is configured to operate tomaintain the voltage at the third node N3 equal or approximately equalto a control voltage on the control voltage terminal 206. Asillustrated, the third node N3 is a common voltage node with respect tothe first and second nodes N1 and N2 because the second input terminalof the differential amplifier 217 includes a high input impedance. As aresult, the voltage at the third node N3 when the resistances of thefirst and second resistances 213 and 214 are approximately equal is anaverage of the voltages on the first and second nodes N1 and N2. Thus,to maintain the third node N3 at a particular voltage, such as thecontrol voltage on the control voltage terminal 206, the amplifier 217may set a particular voltage at N4 even if the voltage on one of thefirst and second nodes N1 and N2 may increase and the voltage on anotherof the first and second nodes N1 and N2 may decrease.

The control circuit 210 may be configured to control the gate voltagesof the third and eighth transistors 222 and 227 to control whether thethird and eighth transistors 222 and 227 conduct or do not conduct usingthe first and second control transistors 211 and 212. For example, withthe voltage at the fourth node N4 relatively stable, the gate voltage ofthe third transistor 222 may be controlled using the first controltransistor 211. When the first control transistor 211 conducts, acurrent may pass through the third resistance 215. The current passingthrough the third resistance 215 may result in a voltage drop across thethird resistance 215. As a result, the gate voltage of the thirdtransistor 222 is the voltage on the fourth node N4 minus the voltagedrop across the third resistance 215. The current through the thirdresistance 215 may be controlled by the second current source 218. Thus,by selecting appropriate values for the current of the second currentsource 218 and the third resistance 215, when the first controltransistor 211 conducts the voltage drop across the third resistance 215may be sufficient such that the gate voltage of the third transistor 222is such that the third transistor 222 does not conduct. In thealternative, when the first control transistor 211 does not conduct,there may not be a voltage drop across the third resistance 215 and thegate voltage of the third transistor 222 may be the voltage on thefourth node N4. The voltage on the fourth node N4 may be sufficient tocause the third transistor 222 to conduct. The control circuit 210 maybe configured to control the gate voltage of the eighth transistor 227using the second control transistor 212 and the fourth resistance 216 ina similar manner as discussed above with respect to the third transistor222.

An example of the operation of the circuit 200 using the illustratedimplementation of the control circuit 210 follows based on the firstinput signal being a logical high and the second input signal being alogical low. In response to the first input signal being a logical high,the gate voltage of the first transistor 220 may be high enough to causethe first transistor 220 to conduct. As the first transistor 220conducts, it may reduce the voltage at the first node N1 such that thesecond transistor 221 conducts. When the second transistor 221 conducts,it may reduce the gate voltages of the fourth and fifth transistors 223and 224 such that the fourth and fifth transistors 223 and 224 conduct.Also, in response to the first input signal being a logical high, thegate voltage of the first control transistor 211 may be high enough tocause the first control transistor 211 to conduct. As a result, currentmay pass through the third resistance 215 resulting in the gate voltageof the third transistor 222 being reduced and the third transistor 222not conducting. Thus, the first output terminal 204 may be raised to thesecond voltage V2.

In response to the second input signal being a logical low, the gatevoltage of the first transistor 220 may be such that the sixthtransistor 225 does not conduct. Additionally, due to the reduction ofthe voltage of the first node N1, the voltage at the second node N2 mayraise to maintain the voltage at node N3 approximately equal to thecontrol voltage on the control voltage terminal 206. As a result, theseventh transistor 226 may not conduct. When the seventh transistor 226does not conduct, the gate voltage of the ninth and tenth transistors228 and 229 are such that the ninth and tenth transistors 228 and 229 donot conduct.

Also, in response to the second input signal being a logical low, thegate voltage of the first control transistor 211 may be such that thefirst control transistor 211 does not conduct. As a result, no currentpasses through the third resistance 215 resulting in the gate voltage ofthe eighth transistor 227 being equal or approximately equal to thevoltage of the fourth node N4 and the eighth transistor 227 conducting.Thus, the second output terminal 205 may be lowered to the first voltageV1. In response to the first input signal switching to a logical low andthe second input signal switching to a logical high, the control circuit210 may be configured to adjust the gate voltages such that the firstoutput signal is a logical low and the second output signal is a logicalhigh in a similar manner as described above.

Modifications, additions, or omissions may be made to the circuit 200without departing from the scope of the present disclosure. For example,additional active or passive circuit elements may be included in thecircuit 200.

FIG. 3A illustrates another example signal conversion circuit 300 (“thecircuit 300”), arranged in accordance with at least some embodimentsdescribed herein. In general, the circuit 300 may be configured toreceive an input differential signal and convert the input differentialsignal to an output differential signal. The output differential signalmay include a voltage swing that is different from a voltage swing ofthe input differential signal. In particular, the voltage swing of theoutput differential signal may be between a ground potential and a firstvoltage and may be greater than the voltage swing of the inputdifferential signal.

The circuit 300 may include first and second input terminals 302 and303, first and second output terminals 304 and 305, a control voltageterminal 306, a control circuit 310, first, second, third, fourth,fifth, sixth, seventh, eighth, ninth, and tenth transistors 320-329,referred to herein collectively as the transistors 320-329, and a firstcurrent source 340.

Each of the transistors 320-329 may include a gate terminal, a sourceterminal, and a drain terminal. As illustrated in FIG. 3A, the sourceterminal may be the terminal with the arrow, the gate terminal may bethe terminal with the parallel horizontal lines, and the drain terminalmay be the other terminal. As illustrated in FIG. 3A, the first, second,third, sixth, seventh, and eighth transistors 320, 321, 322, 325, 326,and 327 may include p-type transistors. The fourth, fifth, ninth, andtenth transistors 323, 324, 328, and 329 may include n-type transistors.

A gate terminal of the first transistor 320 may be coupled to the firstinput terminal 302. A source terminal of the first transistor 320 may becoupled to the first current source 340. A drain terminal of the firsttransistor 320 may be coupled to a source terminal of the secondtransistor 321.

A gate terminal of the second transistor 321 may be coupled to thecontrol circuit 310. A drain terminal of the second transistor 321 maybe coupled to a drain terminal of the fifth transistor 324, a gate ofthe fifth transistor 324, and to a gate of the fourth transistor 323.Source terminals of the fourth and fifth transistors 323 and 324 may becoupled to ground. A drain terminal of the fourth transistor 323 may becoupled to the first output terminal 304 and to a drain terminal of thethird transistor 322. A gate terminal of the third transistor 322 may becoupled to the control circuit 310. A source terminal of the thirdtransistor 322 may be coupled to the first voltage V1. The first voltageV1 may be higher than ground and lower than a second voltage V2 coupledto the first current source 340.

A gate terminal of the sixth transistor 325 may be coupled to the secondinput terminal 303. A source terminal of the sixth transistor 325 may becoupled to the first current source 340. A drain terminal of the sixthtransistor 325 may be coupled to a source terminal of the seventhtransistor 326.

A gate terminal of the seventh transistor 326 may be coupled to thecontrol circuit 310. A drain terminal of the seventh transistor 326 maybe coupled to a drain terminal of the ninth transistor 328, a gate ofthe ninth transistor 328, and to a gate of the tenth transistor 329.Source terminals of the ninth and tenth transistors 328 and 329 may becoupled to ground. A drain terminal of the tenth transistor 329 may becoupled to the second output terminal 305 and to a drain terminal of theeighth transistor 327. A gate terminal of the eighth transistor 327 maybe coupled to the control circuit 310. A source terminal of the eighthtransistor 327 may be coupled to the first voltage V1.

The control circuit 310 may be coupled to the first and second inputterminals 302 and 303 and to the control voltage terminal 306. Thecontrol circuit 310 may be configured to control gate voltages of thethird and eighth transistors 322 and 327 to control whether the thirdand eighth transistors 322 and 327 conduct or do not conduct. Thecontrol circuit 310 may also be configured to control the gate voltagesof the second and seventh transistors 321 and 326 to control whether thesecond and seventh transistors 321 and 326 conduct or do not conduct. Bycontrolling when the second, third, seventh, and eighth transistors 321,322, 326, and 327 conduct, the control circuit 310 may control thegeneration of the output differential signal that is output on the firstand second output terminals 304 and 305.

In particular, the control circuit 310 may be configured to adjust thegate voltages of the second, third, seventh, and eighth transistors 321,322, 326, and 327 based on the input differential signal to control thegeneration of the output differential signal. For example, the inputdifferential signal may include first and second input signals. Thecontrol circuit 310 may adjust the gate voltages of the second and thirdtransistors 321 and 322 based on a logical level of the first inputsignal to generate a first output signal of the output differentialsignal that is output on the first output terminal 304. The controlcircuit 310 may also adjust the gate voltages of the seventh and eighthtransistors 326 and 327 based on a logical level of the second inputsignal to generate a second output signal of the output differentialsignal that is output on the second output terminal 305.

In these and other embodiments, the control circuit 310 may adjust thegate voltages of the second, third, seventh, and eighth transistors 321,322, 326, and 327 based on the input differential signal such that theoutput differential signal includes a signal pattern that corresponds toa signal pattern of the input differential signal. In these and otherembodiments, a corresponding signal pattern may indicate that the outputdifferential signal includes logical highs and logical lows that matchor are an inverse of the logical highs and logical lows of the inputdifferential signal.

An example of the operation of the circuit 300 follows based on thefirst input signal being a logical high and the second input signalbeing a logical low. The first input signal may be received by thecontrol circuit 310. When the first input signal is a logical high, thecontrol circuit 310 may adjust the gate voltage of the third transistor322 such that the third transistor 322 may conduct current from itssource terminal to its drain terminal, raising the voltage at the firstoutput terminal 304 to first voltage V1. The control circuit 310 mayalso adjust the gate voltage of the second transistor 321 such that thesecond transistor 321 does not conduct. The logical high at the gateterminal of the first transistor 320 may also cause the first transistor320 to not conduct. The fifth transistor 324 with its gate terminalcoupled to its drain terminal and with the first and second transistors320 and 321 not conducting may also not conduct such that no currentflows from the second voltage V2 through the first current source 340 toground through the first, second, and fifth transistors 320, 321, and324. The fourth transistor 323 may be in a current mirror configurationwith the fifth transistor 324. As a result, when the fifth transistor324 does not conduct, the fourth transistor 323 may also not conduct.When the fourth transistor 323 does not conduct, it may provide a highimpedance at its drain terminal coupled to the first output terminal304.

When the second input signal is a logical low, the control circuit 310may adjust the gate voltage of the seventh transistor 326 such that theseventh transistor 326 conducts. Furthermore, the logical low at thegate terminal of the sixth transistor 325 may cause the sixth transistor325 to conduct. As a result, the ninth transistor 328 conducts. Thetenth transistor 329 may be in a current mirror configuration with theninth transistor 328 and thus may conduct. As a result, the voltage atthe second output terminal 305 may drop to ground.

Furthermore, when the second input signal is a logical low, the controlcircuit 310 may adjust the gate voltage of the seventh transistor 326such that the seventh transistor 326 does not conduct. Thus, the secondoutput signal may be output as a logical low and the voltage swing ofthe output differential signal may be the difference between the firstvoltage V1 and ground. In response to the first input signal switchingto a logical low and the second input signal switching to a logicalhigh, the control circuit 310 may be configured to adjust the gatevoltages such that the first output signal is a logical low and thesecond output signal is a logical high in a similar manner as describedabove.

Modifications, additions, or omissions may be made to the circuit 300without departing from the scope of the present disclosure. For example,additional active or passive circuit elements may be included in thecircuit 300. Alternately or additionally, the circuit 300 may include aduty cycle sense circuit that may operate in a similar manner as theduty cycle sense circuit 230 of FIGS. 2A and 2B.

FIG. 3B illustrates an example implementation of the control circuit 310of the signal conversion circuit 300 of FIG. 3A, arranged in accordancewith at least some embodiments described herein. The control circuit 310may include a first control transistor 311, a second control transistor312, a first resistance 313, a second resistance 314, a third resistance315, a fourth resistance 316, a differential amplifier 317, and a secondcurrent source 318.

Each of the control transistors 311 and 312 may include a gate terminal,a source terminal, and a drain terminal. As illustrated in FIG. 3B, thesource terminal may be the terminal with the arrow, the gate terminalmay be the terminal with the parallel horizontal lines, and the drainterminal may be the other terminal. As illustrated in FIG. 3B, thecontrol transistors 311 and 312 may be p-type transistors.

A gate terminal of the first control transistor 311 may be coupled tothe first input terminal 302. A source terminal of the first controltransistor 311 may be coupled to the second current source 318. Thedrain terminal of the first control transistor 311 may be coupled to thegate terminal of the third transistor 322 and to a first end of thethird resistance 315. A second end of the third resistance 315 may becoupled to a fourth node N4 to which the gate terminals of the secondand sixth transistors 321 and 325 and an output terminal of thedifferential amplifier 317 are also coupled.

A gate terminal of the second control transistor 312 may be coupled tothe second input terminal 303. A source terminal of the second controltransistor 312 may be coupled to the second current source 318. Thedrain terminal of the second control transistor 312 may be coupled tothe gate terminal of the eighth transistor 327 and to a first end of thefourth resistance 316. The second end of the fourth resistance 316 maybe coupled to the fourth node N4.

A first end of the first resistance 313 may be coupled to the drainterminal of the first transistor 320 and the source terminal of thesecond transistor 321 at a first node N1. The second end of the firstresistance 313 may be coupled to a second end of the second resistance314 and to a first input terminal of the differential amplifier 317 at athird node N3. The first end of the second resistance 314 may be coupledto the drain terminal of the sixth transistor 325 and the sourceterminal of the seventh transistor 326 at a second node N2. A secondinput terminal of the differential amplifier 317 may be coupled to thecontrol voltage terminal 306.

In general, the differential amplifier 317 is configured to operate tomaintain the voltage at the third node N3 equal or approximately equalto a control voltage on the control voltage terminal 306 in an analogousmanner as the differential amplifier 217 of FIG. 2B is configured tooperate to maintain the voltage at the third node N3 equal orapproximately equal to a control voltage on the control voltage terminal206.

The control circuit 310 may be configured to control the gate voltagesof the third and eighth transistors 322 and 327 to control whether thethird and eighth transistors 322 and 327 conduct or do not conduct usingthe first and second control transistors 311 and 312. For example, withthe voltage at the fourth node N4 relatively stable, the gate voltage ofthe third transistor 322 may be controlled using the first controltransistor 311. When the first control transistor 311 conducts, acurrent may pass through the third resistance 315. The current passingthrough the third resistance 315 may result in a voltage drop across thethird resistance 315. As a result, the gate voltage of the thirdtransistor 322 is the voltage on the fourth node N4 plus the voltagedrop across the third resistance 315. The current through the thirdresistance 315 may be controlled by the second current source 318. Thus,by selecting appropriate values for the current of the second currentsource 318 and the third resistance 315, when the first controltransistor 311 conducts, the voltage drop across the third resistance315 may be sufficient such that the gate voltage of the third transistor322 is such that the third transistor 322 does not conduct. In thealternative, when the first control transistor 311 does not conduct,there may not be a voltage drop across the third resistance 315 and thegate voltage of the third transistor 322 may be the voltage on thefourth node N4. The voltage on the fourth node N4 may be sufficient tocause the third transistor 322 to conduct. The control circuit 310 maybe configured to control the gate voltage of the eighth transistor 327using the second control transistor 312 and the fourth resistance 316 ina similar manner as discussed above with respect to the third transistor322.

Modifications, additions, or omissions may be made to the circuit 300without departing from the scope of the present disclosure. For example,additional active or passive circuit elements may be included in thecircuit 300. Alternately or additionally, the circuit 300 may include aduty cycle sense circuit that may operate in a similar manner as theduty cycle sense circuit 230 of FIGS. 2A and 2B.

In FIGS. 1A, 2A, 2B, 3A, and 3B, the illustrated transistors areillustrated as metal-oxide-semiconductor field-effect transistor(MOSFET) transistors. The above description uses the nomenclature gate,source, and drain to represent different terminals of the transistors.The use of the names gate, source, and drain may be used to describegenerically the terminals of a MOSFET transistor, or other types oftransistors, such as bipolar junction transistors (BJT), junction gatefield-effect transistors (JFET), and insulated gate bipolar transistors.Furthermore, p-channel transistors or some combination of re-channel andp-channel transistors may also be used.

FIG. 4 is a perspective view of an example optoelectronic module 400(hereinafter “module 400”) that may include a signal conversion circuit420, arranged in accordance with at least some embodiments describedherein. The module 400 may be configured for use in transmitting andreceiving optical signals in connection with a host device (not shown).

As illustrated, the module 400 may include, but is not limited to, abottom housing 402, a receive port 404, and a transmit port 406, bothdefined in the bottom housing 402; a PCB 408 positioned within thebottom housing 402, the PCB 408 having the signal conversion circuit 420positioned thereon; and a receiver optical subassembly (ROSA) 410 and atransmitter optical subassembly (TOSA) 412 also positioned within thebottom housing 402. An edge connector 414 may be located on an end ofthe PCB 408 to enable the module 400 to electrically interface with thehost device. As such, the PCB 408 facilitates electrical communicationbetween the host device and the ROSA 410 and the TOSA 412.

The module 400 may be configured for optical signal transmission andreception at a variety of data rates including, but not limited to, 1Gb/s, 10 Gb/s, 20 Gb/s, 40 Gb/s, 100 Gb/s, or higher. Furthermore, themodule 400 may be configured for optical signal transmission andreception at various distinct wavelengths using wavelength divisionmultiplexing (WDM) using one of various WDM schemes, such as Coarse WDM,Dense WDM, or Light WDM.

Furthermore, the module 400 may be configured to support variouscommunication protocols including, but not limited to, Fibre Channel andHigh Speed Ethernet. In addition, although illustrated in a particularform factor in FIG. 4, more generally, the module 400 may be configuredin any of a variety of different form factors including, but not limitedto, the Small Form-factor Pluggable (SFP), the enhanced SmallForm-factor Pluggable (SFP+), the 10 Gigabit Small Form-factor Pluggable(XFP), the C Form-factor Pluggable (CFP), and the Quad Small Form-factorPluggable (QSFP) multi-source agreements (MSAs).

The ROSA 410 may house one or more optical receivers, such asphotodiodes, that are electrically coupled to an electrical interface416. The one or more optical receivers may be configured to convertoptical signals received through the receive port 404 into correspondingelectrical signals that are relayed to the host device through theelectrical interface 416 and the PCB 408. The TOSA 412 may house one ormore optical transmitters, such as lasers, that are electrically coupledto another electrical interface 418. The one or more opticaltransmitters may be configured to convert electrical signals receivedfrom the host device by way of the PCB 408 and the electrical interface418 into corresponding optical signals that are transmitted through thetransmit port 406. In some embodiments, the TOSA 412 may receive signalsat a first voltage swing and may convert the signals to have a secondvoltage swing using a signal conversion circuit, such as one of thesignal conversion circuits 100, 200, or 300 of FIGS. 1A, 2A, 2B, 3A, and3B. For example, the TOSA 412 may receive a CML signal and may convertthe CML signal to a CMOS signal that may be used to control amach-zehnder modulator or some other component in the TOSA 412.

The module 400 illustrated with respect to FIG. 4 is one architecture inwhich embodiments of the present disclosure may be employed. It shouldbe understood that this specific architecture is only one of countlessarchitectures in which embodiments may be employed. The scope of thepresent disclosure is not intended to be limited to any particulararchitecture or environment.

In some embodiments, a circuit may include an output terminal; an inputterminal configured to receive an input signal with a first voltageswing; and a first transistor including a first gate terminal, a firstsource terminal, and a first drain terminal.

The circuit may also include a second transistor including a second gateterminal, a second source terminal, and a second drain terminal, thesecond drain terminal coupled to the output terminal and the secondsource terminal coupled to a first voltage; a third transistor includinga third gate terminal, a third source terminal, and a third drainterminal, the third drain terminal coupled to the output terminal, thethird source terminal coupled to a second voltage, and the third gateterminal coupled to the first drain terminal; and a control circuitcoupled to the input terminal, the first gate terminal, and the secondgate terminal, the control circuit configured to adjust voltagesprovided to the first gate terminal and the second gate terminal basedon the input signal such that the second transistor conducts in responseto the input signal being at a first logical level and the thirdtransistor conducts in response to the input signal being at a secondlogical level to generate an output signal output on the outputterminal, wherein a second voltage swing of the output signal isdifferent from the first voltage swing of the input signal.

In one or more of the above embodiments, a middle voltage of the firstvoltage swing is offset from a middle voltage of the second voltageswing.

In one or more of the above embodiments, the second voltage swing isbetween the first voltage and the second voltage and the second voltageis at ground potential.

In one or more of the above embodiments, the circuit further includes aduty cycle sense circuit coupled to the output terminal, the duty cyclesense circuit configured to detect a duty cycle of the output signal andto provide an indication of the detected duty cycle to the controlcircuit.

In one or more of the above embodiments, the control circuit is furtherconfigured to adjust the voltages provided to the first gate terminal,the first source terminal, and the second gate terminal based on theinput signal and the indication of the detected duty cycle to generatethe output signal with an adjusted duty cycle.

In one or more of the above embodiments, the circuit further includes acontrol terminal configured to receive a control signal, wherein thecontrol terminal is coupled to the control circuit and the controlcircuit is configured to adjust a duty cycle of the output signal basedon the control signal.

In one or more of the above embodiments, the control signal is a voltagesignal.

In one or more of the above embodiments, the input signal is a firstsignal of a current-mode-logic differential signal and the output signalis a first signal of a complementary metal-oxide semiconductordifferential signal.

In one or more of the above embodiments, the circuit further includes afirst intermediate transistor including a first intermediate gateterminal, a first intermediate source terminal, and a first intermediatedrain terminal, the first intermediate drain terminal coupled to thefirst drain terminal, the first intermediate gate terminal, and thethird gate terminal and the first intermediate source terminal coupledto the second voltage; and a second intermediate transistor including asecond intermediate gate terminal, a second intermediate sourceterminal, and a second intermediate drain terminal, the secondintermediate drain terminal coupled to the first source terminal and thesecond intermediate gate terminal coupled to the input terminal.

In one or more of the above embodiments, the circuit further includes asecond output terminal; a second input terminal configured to receive asecond input signal with a first voltage swing, wherein the input signaland the second input signal form an input differential signal; a fourthtransistor including a fourth gate terminal, a fourth source terminal,and a fourth drain terminal; a fifth transistor including a fifth gateterminal, a fifth source terminal, and a fifth drain terminal, the fifthdrain terminal coupled to the second output terminal and the fifthsource terminal coupled to the first voltage; and a sixth transistorincluding a sixth gate terminal, a sixth source terminal, and a sixthdrain terminal, the sixth drain terminal coupled to the second outputterminal, the sixth source terminal coupled to the second voltage, andthe sixth gate terminal coupled to the fourth drain terminal, whereinthe control circuit is further coupled to the second input terminal, thefourth gate terminal, and the fifth gate terminal, the control circuitconfigured to adjust voltages provided to the fourth gate terminal andthe fifth gate terminal based on the second input signal such that thefourth transistor conducts in response to the second input signal beingat the first logical level and the fifth transistor conducts in responseto the second input signal being at the second logical level to generatea second output signal output on the second output terminal, wherein theoutput signal and the second output signal form an output differentialsignal.

In some embodiments, a circuit may include an input terminal configuredto receive an input signal with a first voltage swing; an outputterminal configured to output an output signal with a second voltageswing that is different than the first voltage swing; a first transistorthat includes a first gate terminal and a first drain terminal, thefirst gate terminal coupled to the input terminal; a second transistorthat includes a second gate terminal, a second source terminal, and asecond drain terminal, the second source terminal coupled to the firstdrain terminal; an amplifier that includes first and second amplifierinput terminals and an amplifier output terminal, the amplifier outputterminal coupled to the second gate terminal and the first amplifierinput terminal configured to receive a control voltage; a firstresistance between the second source terminal and the second amplifierinput terminal; a third transistor including a third gate terminal, athird source terminal, and a third drain terminal, the third sourceterminal coupled to a first voltage, the third drain terminal coupled tothe output terminal; a second resistance coupled between the third gateterminal and the amplifier output terminal; and a fourth transistorincluding a fourth gate terminal, a fourth source terminal, and a fourthdrain terminal, the fourth source terminal coupled to a second voltage,the fourth drain terminal coupled to the output terminal, and the fourthgate terminal coupled to the second drain terminal.

In one or more of the above embodiments, the control voltage isapproximately equal to the second voltage.

In one or more of the above embodiments, the amplifier is configured tocontrol a gate voltage at the second gate terminal of the secondtransistor to maintain an amplifier input voltage approximately equal tothe control voltage.

In one or more of the above embodiments, the first voltage isapproximately ground potential and the second voltage swing of theoutput signal is between the first voltage and the second voltage,wherein the second voltage swing is larger than the first voltage swing.

In one or more of the above embodiments, the fourth transistor is an-type metal-oxide-semiconductor field-effect transistor and the first,second, and third transistors are p-type metal-oxide-semiconductorfield-effect transistors.

In one or more of the above embodiments, the second voltage swing of theoutput signal is between the first voltage and the second voltage and amiddle point of the second voltage swing is higher than a middle pointof the first voltage swing.

In one or more of the above embodiments, the fourth transistor is ap-type metal-oxide-semiconductor field-effect transistor and the first,second, and third transistors are n-type metal-oxide-semiconductorfield-effect transistors.

In one or more of the above embodiments, the circuit further includes afifth transistor that includes a fifth gate terminal, a fifth sourceterminal, and a fifth drain terminal, the fifth drain terminal coupledto the second drain terminal, the fifth gate terminal, and the fourthgate terminal and the fifth source terminal coupled to the secondvoltage; and a sixth transistor that includes a sixth gate terminal, asixth source terminal, and a sixth drain terminal, the sixth drainterminal coupled to the third gate terminal, the sixth gate terminalcoupled to the input terminal, and the sixth source terminal coupled toa current source.

In one or more of the above embodiments, the circuit further includes asecond input terminal configured to receive a second input signal withthe first voltage swing, wherein the input signal and the second inputsignal form an output differential signal; a second output terminalconfigured to output a second output signal with the second voltageswing, wherein the output signal and the second output signal form anoutput differential signal; a fifth transistor that includes a fifthgate terminal and a fifth drain terminal, the fifth gate terminalcoupled to the second input terminal; a sixth transistor that includes asixth gate terminal, a sixth source terminal, and a sixth drainterminal, the sixth source terminal coupled to the fifth drain terminal;a third resistance between the sixth source terminal and the secondamplifier input terminal; a seventh transistor that includes a seventhgate terminal, a seventh source terminal, and a seventh drain terminal,the seventh source terminal coupled to the first voltage and the seventhdrain terminal coupled to the second output terminal; a fourthresistance coupled between the seventh gate terminal and the amplifieroutput terminal; and an eighth transistor that includes an eighth gateterminal, an eighth source terminal, and an eighth drain terminal, theeighth source terminal coupled to the second voltage, the eighth drainterminal coupled to the second output terminal; and the eighth gateterminal coupled to the sixth drain terminal.

In one or more of the above embodiments, the input signal is a firstsignal of a current-mode-logic differential signal and the output signalis a first signal of a complementary metal-oxide semiconductordifferential signal.

Terms used herein and especially in the appended claims (e.g., bodies ofthe appended claims) are generally intended as “open” terms (e.g., theterm “including” should be interpreted as “including, but not limitedto,” the term “having” should be interpreted as “having at least,” theterm “includes” should be interpreted as “includes, but is not limitedto,” etc.).

Additionally, if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations.

In addition, even if a specific number of an introduced claim recitationis explicitly recited, those skilled in the art will recognize that suchrecitation should be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, means at least two recitations, or two or more recitations).Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” or “one or more of A, B, and C, etc.” isused, in general such a construction is intended to include A alone, Balone, C alone, A and B together, A and C together, B and C together, orA, B, and C together, etc. For example, the use of the term “and/or” isintended to be construed in this manner.

Further, any disjunctive word or phrase presenting two or morealternative terms, whether in the description of embodiments, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” should be understood to include thepossibilities of “A” or “B” or “A and B.”

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the invention andthe concepts contributed by the inventor to furthering the art, and areto be construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present inventionshave been described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A circuit, comprising: an output terminal; aninput terminal configured to receive an input signal with a firstvoltage swing; a first transistor including a first gate terminal, afirst source terminal, and a first drain terminal; a second transistorincluding a second gate terminal, a second source terminal, and a seconddrain terminal, the second drain terminal coupled to the output terminaland the second source terminal coupled to a first voltage; a thirdtransistor including a third gate terminal, a third source terminal, anda third drain terminal, the third drain terminal coupled to the outputterminal, the third source terminal coupled to a second voltage, and thethird gate terminal coupled to the first drain terminal; and a controlcircuit coupled to the input terminal, the first gate terminal, and thesecond gate terminal, the control circuit configured to adjust voltagesprovided to the first gate terminal and the second gate terminal basedon the input signal such that the second transistor conducts in responseto the input signal being at a first logical level and the thirdtransistor conducts in response to the input signal being at a secondlogical level to generate an output signal output on the outputterminal, wherein a second voltage swing of the output signal isdifferent from the first voltage swing of the input signal.
 2. Thecircuit of claim 1, wherein a middle voltage of the first voltage swingis offset from a middle voltage of the second voltage swing.
 3. Thecircuit of claim 2, wherein the second voltage swing is between thefirst voltage and the second voltage and the second voltage is at groundpotential.
 4. The circuit of claim 1, further comprising a duty cyclesense circuit coupled to the output terminal, the duty cycle sensecircuit configured to detect a duty cycle of the output signal and toprovide an indication of the detected duty cycle to the control circuit.5. The circuit of claim 4, wherein the control circuit is furtherconfigured to adjust the voltages provided to the first gate terminal,the first source terminal, and the second gate terminal based on theinput signal and the indication of the detected duty cycle to generatethe output signal with an adjusted duty cycle.
 6. The circuit of claim1, further comprising a control terminal configured to receive a controlsignal, wherein the control terminal is coupled to the control circuitand the control circuit is configured to adjust a duty cycle of theoutput signal based on the control signal.
 7. The circuit of claim 6,wherein the control signal is a voltage signal.
 8. The circuit of claim1, wherein the input signal is a first signal of a current-mode-logicdifferential signal and the output signal is a first signal of acomplementary metal-oxide semiconductor differential signal.
 9. Thecircuit of claim 1, further comprising: a first intermediate transistorincluding a first intermediate gate terminal, a first intermediatesource terminal, and a first intermediate drain terminal, the firstintermediate drain terminal coupled to the first drain terminal, thefirst intermediate gate terminal, and the third gate terminal and thefirst intermediate source terminal coupled to the second voltage; and asecond intermediate transistor including a second intermediate gateterminal, a second intermediate source terminal, and a secondintermediate drain terminal, the second intermediate drain terminalcoupled to the first source terminal and the second intermediate gateterminal coupled to the input terminal.
 10. The circuit of claim 1,further comprising: a second output terminal; a second input terminalconfigured to receive a second input signal with a first voltage swing,wherein the input signal and the second input signal form an inputdifferential signal; a fourth transistor including a fourth gateterminal, a fourth source terminal, and a fourth drain terminal; a fifthtransistor including a fifth gate terminal, a fifth source terminal, anda fifth drain terminal, the fifth drain terminal coupled to the secondoutput terminal and the fifth source terminal coupled to the firstvoltage; and a sixth transistor including a sixth gate terminal, a sixthsource terminal, and a sixth drain terminal, the sixth drain terminalcoupled to the second output terminal, the sixth source terminal coupledto the second voltage, and the sixth gate terminal coupled to the fourthdrain terminal, wherein the control circuit is further coupled to thesecond input terminal, the fourth gate terminal, and the fifth gateterminal, the control circuit configured to adjust voltages provided tothe fourth gate terminal and the fifth gate terminal based on the secondinput signal such that the fourth transistor conducts in response to thesecond input signal being at the first logical level and the fifthtransistor conducts in response to the second input signal being at thesecond logical level to generate a second output signal output on thesecond output terminal, wherein the output signal and the second outputsignal form an output differential signal.
 11. A circuit comprising: aninput terminal configured to receive an input signal with a firstvoltage swing; an output terminal configured to output an output signalwith a second voltage swing that is different than the first voltageswing; a first transistor that includes a first gate terminal and afirst drain terminal, the first gate terminal coupled to the inputterminal; a second transistor that includes a second gate terminal, asecond source terminal, and a second drain terminal, the second sourceterminal coupled to the first drain terminal; an amplifier that includesfirst and second amplifier input terminals and an amplifier outputterminal, the amplifier output terminal coupled to the second gateterminal and the first amplifier input terminal configured to receive acontrol voltage; a first resistance between the second source terminaland the second amplifier input terminal; a third transistor including athird gate terminal, a third source terminal, and a third drainterminal, the third source terminal coupled to a first voltage, thethird drain terminal coupled to the output terminal; a second resistancecoupled between the third gate terminal and the amplifier outputterminal; and a fourth transistor including a fourth gate terminal, afourth source terminal, and a fourth drain terminal, the fourth sourceterminal coupled to a second voltage, the fourth drain terminal coupledto the output terminal, and the fourth gate terminal coupled to thesecond drain terminal.
 12. The circuit of claim 11, wherein the controlvoltage is approximately equal to the second voltage.
 13. The circuit ofclaim 11, wherein the amplifier is configured to control a gate voltageat the second gate terminal of the second transistor to maintain anamplifier input voltage approximately equal to the control voltage. 14.The circuit of claim 11, wherein the first voltage is approximatelyground potential and the second voltage swing of the output signal isbetween the first voltage and the second voltage, wherein the secondvoltage swing is larger than the first voltage swing.
 15. The circuit ofclaim 14, wherein the fourth transistor is a n-typemetal-oxide-semiconductor field-effect transistor and the first, second,and third transistors are p-type metal-oxide-semiconductor field-effecttransistors.
 16. The circuit of claim 11, wherein the second voltageswing of the output signal is between the first voltage and the secondvoltage and a middle point of the second voltage swing is higher than amiddle point of the first voltage swing.
 17. The circuit of claim 16,wherein the fourth transistor is a p-type metal-oxide-semiconductorfield-effect transistor and the first, second, and third transistors aren-type metal-oxide-semiconductor field-effect transistors.
 18. Thecircuit of claim 11, further comprising: a fifth transistor thatincludes a fifth gate terminal, a fifth source terminal, and a fifthdrain terminal, the fifth drain terminal coupled to the second drainterminal, the fifth gate terminal, and the fourth gate terminal and thefifth source terminal coupled to the second voltage; and a sixthtransistor that includes a sixth gate terminal, a sixth source terminal,and a sixth drain terminal, the sixth drain terminal coupled to thethird gate terminal, the sixth gate terminal coupled to the inputterminal, and the sixth source terminal coupled to a current source. 19.The circuit of claim 11, further comprising: a second input terminalconfigured to receive a second input signal with the first voltageswing, wherein the input signal and the second input signal form anoutput differential signal; a second output terminal configured tooutput a second output signal with the second voltage swing, wherein theoutput signal and the second output signal form an output differentialsignal; a fifth transistor that includes a fifth gate terminal and afifth drain terminal, the fifth gate terminal coupled to the secondinput terminal; a sixth transistor that includes a sixth gate terminal,a sixth source terminal, and a sixth drain terminal, the sixth sourceterminal coupled to the fifth drain terminal; a third resistance betweenthe sixth source terminal and the second amplifier input terminal; aseventh transistor that includes a seventh gate terminal, a seventhsource terminal, and a seventh drain terminal, the seventh sourceterminal coupled to the first voltage and the seventh drain terminalcoupled to the second output terminal; a fourth resistance coupledbetween the seventh gate terminal and the amplifier output terminal; andan eighth transistor that includes an eighth gate terminal, an eighthsource terminal, and an eighth drain terminal, the eighth sourceterminal coupled to the second voltage, the eighth drain terminalcoupled to the second output terminal; and the eighth gate terminalcoupled to the sixth drain terminal.
 20. The circuit of claim 11,wherein the input signal is a first signal of a current-mode-logicdifferential signal and the output signal is a first signal of acomplementary metal-oxide semiconductor differential signal.